Technical Field
The present invention relates to a power supply system using an energy storage cell, and more particularly to an energy storage power supply system using a lithium cell.
Related Art
With application of cloud computation and popularization of network storage devices, enterprises and small offices/home offices (SOHOs) have increasing demands for an uninterruptible power supply (UPS). However, an internal power source usually used by a current UPS is a lead-acid cell, which does not meet the developing trend of relevant product technologies. Besides, due to product advantages of a lithium cell, the lithium cell may completely replace the lead-acid cell in the future, and become an internal power source of a new generation UPS.
The UPS is a device which temporarily supplies power for a personal computer and peripherals thereof by using an internal cell as a power source when problems such as power off or change of a power source occur. During a UPS power supply period, the system is terminated to ensure that the system operation ends securely. The UPS is generally provided for SOHOs or enterprises, to enable industrial facilities in the production process such as online server products and electronic apparatuses to be operated stably. Especially, as application of cloud computation is increasingly popularized, many enterprises employ an array-type magnetic disk device or a network attached storage (NAS) as a main storage medium, and have increasing demands for the UPS, which prevents data loss caused by transient power unsteadiness and avoids massive enterprise loss.
The global developing trend of the UPS technology can generally be divided into three parts, namely, energy saving and environmental protection, high efficiency and high reliability, and digitalization, intellectualization, and networking. Therefore, the current and future design focuses of the UPS lie in high efficiency, energy saving, and environment-friendly materials, high reliability, and easy maintenance and management. The internal power source of the current UPS is mainly a lead-acid cell, but the property and characteristics of the lead-acid cell are against the overall developing trend of the UPS technology, and meanwhile, with rise of the production cost of a lead polar plate and the lead-acid cell, it is an inevitable trend that the lithium cell replaces the lead-acid cell to become the internal power source of the UPS.
Compared with the lead-acid cell, the lithium cell has the following advantages which meet the developing trend of the current UPS technology, and is thus more suitable for the UPS.
1. The depth of discharge exceeds 95%, so the discharge time is long, which ensures that systems such as server products complete working before the UPS finishes discharging.
2. A high-rate discharge current is supported, which is suitable for high power application scenarios.
3. The discharge voltage is stable, which avoids facility failure due to unstable voltage.
4. The self-discharge rate is low. The self-discharge rate of the lithium cell is only 1% to 1.5% per month, which is far superior to that of the lead-acid cell (the self-discharge rate thereof is 30%). In scenarios where the power is stable, an uninterruptible power system does not need to perform trickling charge of the cell at any time for maintenance, thereby achieving the purpose of energy saving.
5. The service life is long. The lithium-iron cell can still maintain 75% of the original capacity after being charged and discharged for 3,000 times. The service life of the lithium-iron cell is ten times that of the lead-acid cell, and the lithium-iron cell is maintenance-free, so the maintenance cost of the cell can be largely reduced.
6. The security is high, and there is no risk of acid leakage.
7. The raw material of the lithium cell is an environment-friendly material, which contains no heavy metal or high contamination substances.
Due to their different characteristics, the lithium cell and the lead-acid cell have different charging curves and loops, and the charging apparatuses have different specifications in accordance with UPSs of different brands, so it is a huge project to replace the lead-acid cell with the lithium cell for an existing UPS client each year. Taking a conventional cell system for example, the cell system is formed of several cell modules connected in series. Each cell module has a built-in cell set voltage monitoring function, used for monitoring voltage of a single cell set (equivalent to voltage of a single cell). When the voltage of a random cell set is over high or over low, the cell module sends a signal indicating overcharge or low voltage. However, the transmission specification of the monitoring signal may cause problems in reliability and compatibility with an existing UPS system (taking a UPS as an example). Therefore, the present invention is directed to facilitate replacement of an existing lead-acid cell with a lithium cell module and make the lithium cell module compatible with an existing UPS system.